1. Field of the Invention
This invention relates to a hand-written character recognition device for extracting a feature of a hand-written character written on a tablet on the basis of coordinate data of the written character so as to recognize the character, and more particularly to a hand-written character recognition device having means for removing a noise which appears as a sudden variation of coordinate data written on the tablet.
2. Description of the Prior Art
There is known a hand-written character recognition device which is equipped with a character input device such as a tablet (x-y coordinate input unit) having sensors arranged in a matrix form and extracts a character feature on the basis of x-y coordinate data of a character written on the tablet, thereby recognizing the hand-written character.
FIG. 1 is a block diagram showing the basic construction of the hand-written character recognition device. As shown in FIG. 1, the hand-written character recognition device includes a tablet 100, a pre-processing unit 101, a feature extraction unit 102, and a character recognition unit 103. The tablet 100 has an input portion having a sensor system of one of a touch-panel type sensor which is a pressure-sensitive type sensor using a plane resistor, an electrostatic coupling type sensor or a power source induction type sensor, and serves to output x-y coordinate data of a hand-written character. The pre-processing unit successively receives the x-y coordinate data outputted from the tablet 100 at every predetermined time to define x-y coordinate points of the hand-written character. The feature extraction unit 102 extracts a stroke feature of the inputted character using the data of the x-y coordinate points which has been defined in the pre-processing unit 101. The character recognition unit 103 analyzes the inputted stroke feature obtained by the feature extraction processing in the feature extraction unit 102 so as to recognize the inputted character, and then generates a character code for the inputted character.
In a write operation of a character on the tablet 100, in accordance with the resolution of the tablet and input unit, a plurality of coordinate points would be detected in x and y directions for one data. Therefore, when a plurality of coordinate points are detected for one data, in the pre-processing unit 101, a midpoint of these plurality of coordinate points is calculated so as to define an effective x-y coordinate point of the hand-written character used for the subsequent feature extraction.
However, in such a hand-written character recognition device, especially when a character is written through a finger, a plurality of coordinate points are detected in each of x and y directions. In addition, a write speed and a write pressure are not necessarily constant (that is, the write-in operation is not necessarily stably carried out). Therefore, the calculated x-y coordinate points defined in the pre-processing unit includes some x-y coordinate points deviated from the actual locus of the hand-written character (hereinafter referred to as "noise data" or "noise coordinate point"). The frequent occurrence of the noise data causes the feature extraction processing for the input stroke to be more complicated and unreliable.